1. Field of the Invention
The present invention concerns a method and a device for determining the pressure in the combustion chamber of an internal combustion engine, in particular a spontaneous ignition engine.
The present invention also concerns a method and a device for controlling fuel injection in an internal combustion engine, in particular a spontaneous ignition engine, using said method for determining the pressure in the combustion chamber.
2. Description of the Related Art
As is known, the cars currently on the market are equipped with a complex and sophisticated control system that is able to implement complex control strategies with the aim of optimizing, on the basis of information received from physical on-board sensors, certain important engine quantities such as consumption, exhaust emission levels, engine torque, and acoustic noise produced by the engine.
In general, the cost limits imposed by the automobile market on cars make it practically impossible to adopt closed-loop control strategies, which can be achieved only for research purposes in specially set-up laboratories, and allow only the adoption of open-loop control strategies operating on the basis of maps memorized in the electronic control unit and experimentally defined on the work-bench during the engine design phase, with all the consequences that may ensue from the absence of feedback, such as poor reliability and unsatisfactory performances.
The closed-loop control achieved in the laboratory operates on the basis of the pressure value in the combustion chamber, since all the above-mentioned engine quantities to be optimized can be derived from this, and the pressure value in the combustion chamber is measured by means of a dynamic pressure sensor arranged in the combustion chamber and able to follow the sudden pressure variations in the engine cycle.
FIG. 1 shows a schematic block diagram of a typical closed-loop control system used in a research laboratory. In particular, in FIG. 1 is indicated with 1 a Diesel engine equipped with an electronically controlled fuel injection system 2, that is a fuel injection system 2 of the type comprising one or more electro-injectors 3, each for injecting fuel in a respective cylinder of the engine under the control of an electronic control unit (ECU) 4. In this type of injection system, the instantaneous flow rate of fuel to be injected ROI (“Rate Of Injection”) is adjusted by the electronic control unit 4 on the basis of reference values of engine quantities to be optimized, such as consumption, exhaust emission levels, engine torque, acoustic noise, all of which can be indirectly obtained from the pressure in the combustion chamber. In turn, the pressure in the combustion chamber is measured by means of a dynamic pressure sensor 5 arranged in the combustion chamber and generating a pressure signal which is then processed either by a dedicated electronic device 6, as shown in FIG. 1, or directly by the electronic control unit 4 in order to assess by how much the actual values of the quantities to be optimized differ from the reference values. This information is then used by the electronic control unit 4 to choose the most suitable injection law to be implemented in the next engine cycle to optimize the above-mentioned engine quantities.
However, the closed-loop control described above is applicable only in the laboratory on experimental prototypes and cannot at the moment be adopted on cars intended for the market due not only to the high cost of the dynamic pressure sensor but above all due to the numerous problems deriving from the use of the pressure sensor such as its bulk in the combustion chamber, the need for its periodic maintenance and replacement due to wear, since it is subject to the high pressures and temperatures present in the combustion chamber, replacement which, inter alia, would require an estimate of its average life cycle, and last but not least the need to provide a specific electronic device that manages it (an amplifier, a sophisticated filter, a current-voltage-pressure converter).